Methods of forming polycrystalline compacts

ABSTRACT

Methods of forming a polycrystalline compact for use in an earth-boring tool include sintering a plurality of hard particles with catalyst material to form a polycrystalline material that includes a plurality of inter-bonded particles of hard material integrally formed with the catalyst material and introducing at least a portion of the polycrystalline material to a reactive material to remove at least a portion of the catalyst material contained within the polycrystalline material. The reactive material may include at least one of a molten glass, an ionic compound, a leaching liquor, and a chemical plasma. The reactive material may be introduced to the polycrystalline material at a temperature of greater than or equal to a melting point thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/328,434, filed Apr. 27, 2010, the disclosure ofwhich is hereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to methods offorming such polycrystalline diamond compact cutting elements forearth-boring tools.

BACKGROUND

Earth-boring tools for forming wellbores in subterranean earthformations generally include a plurality of cutting elements secured toa body. For example, fixed-cutter earth-boring rotary drill bits (alsoreferred to as “drag bits”) include a plurality of cutting elements thatare fixedly attached to a bit body of the drill bit. Similarly, rollercone earth-boring rotary drill bits may include cones that are mountedon bearing pins extending from legs of a bit body such that each cone iscapable of rotating about the bearing pin on which it is mounted. Aplurality of cutting elements may be mounted to each cone of the drillbit. In other words, earth-boring tools typically include a bit body towhich cutting elements are attached.

The cutting elements used in such earth-boring tools often includepolycrystalline diamond compacts (often referred to as “polycrystallinediamond compact”), which act as cutting faces of a polycrystallinediamond material. Polycrystalline diamond material is material thatincludes inter-bonded grains or crystals of diamond material. In otherwords, polycrystalline diamond material includes direct, inter-granularbonds between the grains or crystals of diamond material. The terms“grain” and “crystal” are used synonymously and interchangeably herein.

Polycrystalline diamond compact cutting elements are typically formed bysintering and bonding together relatively small diamond grains underconditions of high temperature and high pressure in the presence of acatalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) toform a layer (e.g., a compact or “table”) of polycrystalline diamondmaterial on a cutting element substrate. These processes are oftenreferred to as high temperature/high pressure (HTHP) processes. Thecutting element substrate may comprise a cermet material (i.e., aceramic-metal composite material) such as, for example, cobalt-cementedtungsten carbide. In such instances, the cobalt (or other catalystmaterial) in the cutting element substrate may be swept into the diamondgrains during sintering and serve as the catalyst material for formingthe inter-granular diamond-to-diamond bonds, and the resulting diamondtable, from the diamond grains. In other methods, powdered catalystmaterial may be mixed with the diamond grains prior to sintering thegrains together in an HTHP process.

Upon formation of a diamond table using an HTHP process, catalystmaterial may remain in interstitial spaces between the grains of diamondin the resulting polycrystalline diamond compact. The presence of thecatalyst material in the diamond table may contribute to thermal damagein the diamond table when the cutting element is heated during use, dueto friction at the contact point between the cutting element and theformation.

Polycrystalline diamond compact cutting elements in which the catalystmaterial remains in the polycrystalline diamond compact are generallythermally stable up to a temperature in a range of about from aboutseven hundred fifty degrees Celsius (750° C.), although internal stresswithin the cutting element may begin to develop at temperaturesexceeding about three hundred fifty degrees Celsius (350° C.). Thisinternal stress is at least partially due to differences in the rates ofthermal expansion between the diamond table and the cutting elementsubstrate to which it is bonded. This differential in thermal expansionrates may result in relatively large compressive and tensile stresses atthe interface between the diamond table and the substrate, and may causethe diamond table to delaminate from the substrate. At temperatures ofabout seven hundred fifty degrees Celsius (750° C.) and above, stresseswithin the diamond table itself may increase significantly due todifferences in the coefficients of thermal expansion of the diamondmaterial and the catalyst material within the diamond table. Forexample, cobalt thermally expands significantly faster than diamond,which may cause cracks to form and propagate within the diamond table,eventually leading to deterioration of the diamond table andineffectiveness of the cutting element.

Furthermore, at temperatures at or above about seven hundred fiftydegrees Celsius (750° C.), some of the diamond crystals within thepolycrystalline diamond compact may react with the catalyst materialcausing the diamond crystals to undergo a chemical breakdown orback-conversion to another allotrope of carbon or another carbon-basedmaterial. For example, the diamond crystals may graphitize at thediamond crystal boundaries, which may substantially weaken the diamondtable. In addition, at extremely high temperatures, in addition tographite, some of the diamond crystals may be converted to carbonmonoxide and carbon dioxide.

In order to reduce the problems associated with differential rates ofthermal expansion and chemical breakdown of the diamond crystals inpolycrystalline diamond compact PDC cutting elements, so-called“thermally stable” polycrystalline diamond compacts (which are alsoknown as thermally stable products, or “TSPs”) have been developed. Sucha thermally stable polycrystalline diamond compact may be formed byleaching the catalyst material (e.g., cobalt) out from interstitialspaces between the inter-bonded diamond crystals in the diamond tableusing, for example, an acid or combination of acids (e.g., aqua regia).Thermally stable polycrystalline diamond compacts in which substantiallyall catalyst material has been leached out from the diamond table havebeen reported to be thermally stable up to temperatures of about twelvehundred degrees Celsius (1200° C.).

Examples of conventional acid leaching processes are described in U.S.Pat. No. 6,410,085 to Griffin et al. (issued Jun. 25, 2002), U.S. Pat.No. 6,435,058 to Matthias et al. (issued Aug. 20, 2002), U.S. Pat. No.6,481,511 to Matthias et al. (issued Nov. 19, 2002), U.S. Pat. No.6,544,308 to Griffin et al. (issued Apr. 8, 2003), U.S. Pat. No.6,562,462 to Griffin et al. (issued May 13, 2003), U.S. Pat. No.6,585,064 to Griffin et al. (issued Jul. 1, 2003), U.S. Pat. No.6,589,640 to Griffin et al. (issued Jul. 8, 2003), U.S. Pat. No.6,592,985 to Griffin et al. (issued Jul. 15, 2003), U.S. Pat. No.6,601,662 to Matthias et al. (issued Aug. 5, 2003), U.S. Pat. No.6,739,214 to Matthias et al. (issued May 25, 2004), U.S. Pat. No.6,749,033 to Matthias et al. (issued Jun. 15, 2004) and U.S. Pat. No.6,797,326 to Matthias et al. (issued Sep. 28, 2004). However, such acidleaching processes are problematic because the acid compounds usedtherein are difficult to control in use, problematic to store, requireprolonged exposure times under elevated temperature and, in addition,generate a substantial quantity of hazardous waste.

Furthermore, conventional acid leaching processes often result innon-uniform removal of the catalyst material caused by the aggressiveaction of the acid compounds on polycrystalline material of thepolycrystalline diamond compacts. Such non-uniform removal maycompromise durability and reduce temperature tolerance of thepolycrystalline diamond compacts having the catalyst material removedfrom only a portion thereof. For example, removal of catalyst materialusing conventional acid leaching processes may results in spikes,valleys and variations that extend beyond a depth of the polycrystallinediamond compact to which removal of the catalyst material is desired.

BRIEF SUMMARY

In some embodiments, the present disclosure includes methods of forminga polycrystalline compact for use in an earth-boring tool. Such methodsmay include at least partially melting at least one of a silicate glass,an alkali metal salt, and a rare earth element to form a reactivematerial and introducing the reactive material to a polycrystallinecompact comprising a catalyst material disposed in interstitial spacesbetween inter-bonded crystals of a polycrystalline material to remove atleast a portion of the catalyst material.

In additional embodiments, the present disclosure includes methods offorming a polycrystalline compact cutting element for an earth-boringtool. Such methods may include forming a cutting element comprising apolycrystalline material and a catalyst material disposed ininterstitial spaces between inter-bonded crystals of the polycrystallinematerial and removing at least a portion of the catalyst material fromthe interstitial spaces by exposing at least a portion of thepolycrystalline material to at least one of a solution comprising aceticacid and a chemical plasma comprising an inert gas or an oxidizingagent.

Other features and advantages of the present disclosure will becomeapparent to those of ordinary skill in the art through consideration ofthe ensuing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming which are regarded as embodiments of the presentdisclosure, the advantages of embodiments of the present disclosure maybe more readily ascertained from the following description ofembodiments of the present disclosure when read in conjunction with theaccompanying drawings in which:

FIG. 1 is a flowchart of an embodiment of a method of forming apolycrystalline compact cutting element according to the presentdisclosure;

FIGS. 2A through 2C are illustrations depicting a method of forming apolycrystalline compact cutting element according to the embodiment ofFIG. 1;

FIG. 3A is a simplified figure illustrating how a microstructure of aregion or layer of polycrystalline material of the cutting element shownin FIGS. 2A and 2B may appear under magnification;

FIG. 3B is a simplified figure illustrating how a microstructure of aregion or layer of polycrystalline material of the cutting element shownin FIG. 2C may appear under magnification; and

FIG. 4 is a perspective view of an embodiment of an earth-boring tool ofthe present disclosure that includes a plurality of cutting elementsformed in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views ofany particular material, apparatus, system, or method, but are merelyidealized representations which are employed to describe the presentdisclosure. Additionally, elements common between figures may retain thesame numerical designation.

In some embodiments, methods of the present disclosure may be used tofabricate polycrystalline diamond compact (PDC) cutting elements for usein earth-boring tools, such as drill bits. The methods employ the use ofa non-acidic, reactive material to remove catalyst material from thepolycrystalline material of the PDC that forms the cutting element. Thepolycrystalline material may be formed using a high temperature/highpressure (HTHP) process. In some embodiments, the polycrystallinematerial may be formed on a cutting element substrate, or thepolycrystalline material may be formed separately from any cuttingelement substrate and later attached to a cutting element substrate. Thereactive material may include, for example, a molten glass, an ioniccompound, a leaching liquor or a chemical plasma. Removing the catalystmaterial from the polycrystalline material using the non-acidic,reactive materials disclosed herein may provide improved control of adepth at which the catalyst material is removed.

As used herein, the term “catalyst material” refers to any material thatis capable of substantially catalyzing the formation of inter-granularbonds between grains of hard material during an HTHP but at leastcontributes to the degradation of the inter-granular bonds and granularmaterial under elevated temperatures, pressures, and other conditionsthat may be encountered in a drilling operation for forming a wellborein a subterranean formation. For example, catalyst materials for diamondinclude, by way of example only, cobalt, iron, nickel, other elementsfrom Group VIIIA of the Periodic Table of the Elements, and alloysthereof.

As used herein, the term “drill bit” means and includes any type of bitor tool used for drilling during the formation or enlargement of awellbore and includes, for example, rotary drill bits, percussion bits,core bits, eccentric bits, bi-center bits, reamers, mills, drag bits,roller cone bits, hybrid bits and other drilling bits and tools known inthe art.

As used herein, the term “molten” means and includes a state in which amaterial is viscous and in a softened or melted state through which thematerial passes in transitioning from a solid state to a liquid state.

As used herein, the term “hard material” means and includes any materialhaving a Knoop hardness value of about 3,000 Kg_(f)/mm² (29,420 MPa) ormore. Hard materials include, for example, diamond and cubic boronnitride.

As used herein, the term “inter-granular bond” means and includes anydirect atomic bond (e.g., covalent, metallic, etc.) between atoms inadjacent grains of material.

As used herein, the term “polycrystalline compact” means and includesany structure comprising a polycrystalline material formed by a processthat involves application of pressure (e.g., compaction) to theprecursor material or materials used to form the polycrystallinematerial.

As used herein, the term “polycrystalline material” means and includesany material comprising a plurality of grains or crystals of thematerial that are bonded directly together by inter-granular bonds. Thecrystal structures of the individual grains of the material may berandomly oriented in space within the polycrystalline material.

As used herein, the term “leaching” means and includes removing orextracting materials from a solid material (such as a polycrystallinematerial) into a carrier, such as by dissolving the materials into thecarrier or by converting the materials into a salt.

As used herein with regard to a depth or level, or magnitude of a depthof level, that catalyst is removed beneath a surface of apolycrystalline compact, the term “standard deviation” means andincludes a measure of dispersion or variation obtained by extracting thesquare root of the mean of squared deviations of observed values fromtheir mean in a frequency distribution. A low standard deviationindicates that data points tend to be very close to the mean, whereashigh standard deviation indicates that the data points are spread outover a large range of values. A reduced standard deviation may indicatethat the observed depths of catalyst removal are closer to the mean and,thus, may be referred to herein as an improvement in the standarddeviation (i.e., “improved standard deviation”). To determine animprovement in the standard deviation, a depth at which the catalyst isremoved beneath a surface of the polycrystalline compact may bedetermined using conventional methods, such as, electron microscopy.Using the methods described herein, the standard deviation may beimproved, for example, by up to about 80% and, more particularly, bybetween about 5% and about 20%.

As used herein with regard to a depth or level, or magnitude of a depthof level, beneath a surface of a polycrystalline compact, the terms“substantially uniform” and “substantially uniformly” mean and include adepth of an area under the surface which is substantially devoid ofsignificant aberrations such as spikes and/or valleys in excess of ageneral magnitude of such depth. More specifically, a “substantiallyuniform depth” when referring to a depth of catalyst removal beneath asurface of a polycrystalline compact means and includes a depth of suchremoval substantially free of significant aberrations such as spikes,valleys and other variations in the region below the surface. In otherwords, if catalyst is removed to a substantially uniform depth below,for example, a cutting face of a polycrystalline compact, the catalystis removed from an area below the surface of the cutting face to adepth, the boundary of which with a remainder of the compact includingsuch catalyst while not necessarily constant, is free of significantaberrations such as spikes, valleys and/or other variations.

FIG. 1 is a process flow of an embodiment of a method of the presentdisclosure. The associated structures formed during the process shown inFIG. 1 are illustrated in FIGS. 2A through 2C. Referring to theforegoing drawing figures, in a first act 1, a cutting element 10 (FIG.2A) that includes a polycrystalline material 14 is formed from particlesof a hard material, such as diamond particles (also known as “grit”) inthe presence of a catalyst material 11 using an HTHP process. In someembodiments, the polycrystalline material 14 may be formed on asupporting substrate 12, or may be attached to the supporting substrate12 after formation of the polycrystalline material 14. The substrate 12may comprise a cermet material such as cobalt-cemented tungsten carbide.In a second act 2, a mask, such as fixture 20 (FIG. 2B), may be formedover the substrate 12 and, optionally, a portion of the polycrystallinematerial 14 of the cutting element 10. In a third act 3, at least aportion of the catalyst material 11 may be removed from exposed regionsof the polycrystalline material 14 using a non-acidic, reactivematerial, such as a molten glass material, an ionic compound, a leachingliquor or a chemical plasma, as will be described herein (FIG. 2C).Controlled removal of the catalyst material 11 using the reactivematerial may improve (i.e., reduce) a standard deviation of a depth atwhich the catalyst material 14 is removed from beneath a surface of PCDcutting elements, such as cutting element 10. As used herein, the term“remove” as applied to catalyst material 11 within the polycrystallinematerial 14 means and includes substantial removal of catalyst 11 frominterstitial spaces within the polycrystalline material 14 and fromsurfaces of the bonded particles of which the polycrystalline material14 is comprised, and does not preclude the existence of some smallquantity of catalyst material 11 within the region or regions of thepolycrystalline material 14 from which the catalyst material 11 has beenremoved. Stated another way, the polycrystalline material 14 may have aregion or regions, or even the entirety of the polycrystalline material14, which are rendered substantially free of catalyst material 11 by aremoval process according to an embodiment of the disclosure. Forexample, the standard deviation of the depth at which the catalystmaterial 11 is removed may be improved by between about 5% and about80%, more particularly, between about 10% and about 20% and, moreparticularly still, about 15%. By way of example and not limitation, thereactive material may enable the catalyst material 11 to besubstantially uniformly removed from the polycrystalline material 14.

FIGS. 2A through 2C illustrate an embodiment of a method of the presentdisclosure. FIG. 2A is a perspective view of a cutting element 10 thatmay be used, for example, in an earth-boring tool. The cutting element10 may include a polycrystalline material 14, also referred to in theart as a “polycrystalline diamond table” or a “diamond table.” Thepolycrystalline material 14 of the cutting element 10 may include aplurality of interstitial regions throughout which a catalyst material11 is dispersed. The cutting element 10, 10′ shown in FIGS. 2A though 2Cis formed on a supporting substrate 12 (as shown) of cemented tungstencarbide or other suitable material as known in the art in a conventionalprocess of the type described, by way of non-limiting example, in U.S.Pat. No. 3,745,623 to Wentorf et al. (issued Jul. 17, 1973), or may beformed as a freestanding polycrystalline diamond compact (i.e., withoutthe supporting substrate 12) in a similar conventional process asdescribed, by way of non-limiting example, in U.S. Pat. No. 5,127,923 toBunting et al. (issued Jul. 7, 1992), the disclosure of each of which isincorporated herein in its entirety by this reference. Thepolycrystalline material 14 may be bonded to the supporting substrate 12at an interface 16. A cutting surface 18 of the polycrystalline material14 may be exposed opposite interface 16 as a working surface. While thecutting element 10 in the embodiment depicted in FIG. 2A is cylindricalor disc-shaped, in other embodiments, the cutting element 10 may haveany desirable shape, such as a dome, cone, chisel, etc. Thepolycrystalline material 14 may comprise natural diamond, syntheticdiamond, or a mixture thereof, and may be formed using diamond grit ofdifferent crystal sizes (i.e., from multiple layers of diamond grit,each layer having a different average crystal size or by using a diamondgrit having a multi-modal crystal size distribution).

As shown in FIG. 2B, the cutting element 10 may be masked to protect orshield the substrate 12 and, optionally, a portion of thepolycrystalline material 14 during removal of the catalyst material 11.The cutting element 10 may be masked using a material impervious to thereactive material. For example, the cutting element 10 may be disposedin a fixture 20 to mask the substrate 12 and a portion of thepolycrystalline material 14, if desired. In some embodiments, thefixture 20 may be formed from a heat resistant material, such as aceramic material, a metal material or a metal alloy, or may be formedfrom a chemical resistant material, such as a polymer material orgraphite. As a non-limiting example, the cutting element 10 may befitted in a recess 22 in the fixture 20 by a shrink-fitting process. Thecutting element 10 may be disposed in the recess 22 of the fixture 20such that the cutting surface 18 of the polycrystalline material 14 isexposed. Heat may then be applied to the cutting element 10 within thefixture 20 to cause expansion of the cutting element 10. As the cuttingelement 10 and fixture 20 cool to room temperature, a diameter of therecess 22 in the fixture 20 may be slightly smaller than a diameter ofthe cutting element 10. The fixture 20 may be used to shield portions ofthe cutting element 10 when exposure to the reactive material is notdesired, including the supporting substrate 12 and, optionally, aportion of the polycrystalline material 14. While both the substrate 12and the polycrystalline material 14 of the cutting element 10 aredisposed in the fixture 20 in the embodiment depicted in FIG. 2B, inother embodiments, the polycrystalline material 14 of the cuttingelement 10, or a portion thereof, may protrude above the fixture 20, asshown in broken lines, such that sidewalls of the polycrystallinematerial 14 are exposed for removal of the catalyst material therefromconcurrently with removal of the catalyst material 11 from the cuttingsurface 18. The resulting area of polycrystalline material 14 in such aninstance may be said to form a “cap-like” structure of polycrystallinematerial 14 from which catalyst material 11 has been removed.

FIG. 2C illustrates the cutting element 10′ after removal of thecatalyst material 11 (FIG. 2A) from at least a portion of thepolycrystalline material 14. In some embodiments, at least a portion ofor substantially all of the catalyst material 11 may be removed from thepolycrystalline material 14. In other embodiments, the catalyst material11 is removed from portions of the polycrystalline material 14surrounding the cutting surface 18, as shown in FIG. 2C, and thepolycrystalline material 14 may include two general regions separated atan interface 24. A catalyst-filled portion 26 forms the lower portion ofthe polycrystalline material 14 and may be bonded to the supportingsubstrate 12. A leached portion 28 forms the upper portion of thepolycrystalline material 14 and is adjoined to catalyst-filled portion26 at interface 24. The leached portion 28 of the polycrystallinematerial 14 provides a thermally stable cutting surface 18. In someembodiments, the leached portion 28 includes a polycrystalline material14 having interstitial regions, at least a portion of which aresubstantially free of catalyst material 11. The presently disclosedmethods enable an improvement in the standard deviation (i.e., areduction in an amount of variation) of removal of the catalyst material11 from the polycrystalline material 14, to a desired depth or depths.In other words, in cutting elements subjected to conventional acidleaching processes, the methods of the present disclosure may provide animprovement in the standard deviation of removal of the catalystmaterial 11 from within the polycrystalline material 14 of PDC cuttingelements. For example, the standard deviation of the depth of theleached portion 28 between cutting elements formed using the methods ofthe present disclosure may be improved by about 10% in comparison to astandard deviation in depth of leached portions formed usingconventional acid leaching processes. In addition, the catalyst material11 may be substantially uniformly removed from the cutting surface 18 ofthe polycrystalline material 14 and, optionally, from the sidewalls ofthe polycrystalline material 14. In some embodiments, the catalystmaterial 11 may be removed from a region having a substantially uniformdepth from the cutting surface 18 or the sidewalls of thepolycrystalline material 14. Accordingly, removal of the catalystmaterial 11 using the reactive material as described herein may reduceor eliminate the number and depth of spikes or variations of the leachedportion 28 that extend past a desired depth of the interface 24 betweenthe catalyst-filled portion 26 and the leached portion 28. For example,if the polycrystalline material 14 has a depth of between about 1 mm andabout 3 mm, in one embodiment the catalyst material 11 may be removed orleached from the polycrystalline material 14 to a depth of less thanabout one hundred micrometers (100 μm or 0.1 mm) and, more particularly,between about twenty five micrometers (25 μm or 0.025 mm) and aboutninety-five micrometers (95 μm or 0.095 mm). In another embodiment, thecatalyst material may be removed to a depth of more than about onehundred micrometers (100 μm, or 0.1 mm), for example, to as much as fivehundred micrometers (500 μm or 0.5 mm) or, in one case, to a depthselected from within a range of between about two hundred fiftymicrometers (250 μm or 0.25 mm) and about three hundred micrometers (300μm or 0.3 mm).

The catalyst material 11 may be removed from the interstices of thepolycrystalline material 14 to form the thermally stable cutting surface18 by exposing the polycrystalline material 14 to a reactive material.The reactive material may include, for example, a molten glass, a moltensalt, a leaching liquor, a eutectic liquid or a chemical plasma. In someembodiments, the polycrystalline material 14 or the cutting surface 18thereof may be exposed to the reactive material while the cuttingelement 10 is disposed within the fixture 20 to preclude contact betweenthe reactive material and a shielded region of the polycrystallinematerial 14 and the supporting substrate 12, if present.

In some embodiments, the reactive material may include a glass materialin a molten state. The glass material may be a silicate glass, such as aborosilicate glass, an aluminosilicate glass, a high silica glass,phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG). In someembodiments, a sodium material (also referred to as a “flux material”)may be added to the glass material to substantially reduce a meltingpoint of the glass material. The sodium material may include, forexample, sodium hydroxide, sodium carbonate, sodium borohydrate orsodium chloride. By way of non-limiting example, the glass material mayhave a melting point of less than or equal to about one thousand degreesCelsius (1,000° C.) and, more particularly, between about twenty degreesCelsius (20° C.) and about nine hundred degrees Celsius (900° C.) and,more particularly still, between about three hundred degrees Celsius(300° C.) and about seven hundred fifty degrees Celsius (750° C.). Insome embodiments, the glass material may be introduced to the cuttingelement 10 at a temperature of greater than or equal to about a meltingpoint of the glass material. By way of non-limiting example, the glassmaterial may be introduced to the polycrystalline material 14 of thecutting element 10 in a chamber (not shown) of a conventional furnace orreactor. A temperature within the chamber may be controlled to maintainthe glass material in a molten state during the removal of the catalystmaterial 11 from the polycrystalline material 14. In other embodiments,the glass material may be heated to a molten state and thepolycrystalline material 14 of the cutting element 10 may be immersed inthe molten glass material or may be inverted and dipped into the moltenglass material. In the molten state, the glass material may corrode,dissolve or otherwise remove the catalyst material 11 from a portion ofthe polycrystalline material 14 such that at least a portion of theinterstices of the portion of the polycrystalline material 14 aresubstantially free of catalyst material 11.

In other embodiments, the reactive material may include an ioniccompound such as, a salt, a mixture of salts or a mixture of compoundsthat may produce a salt. The ionic compounds may be selected toselectively dissolve the catalyst material 11 with respect to thepolycrystalline material 14. The ionic compound may be a salt of, forexample, an alkali metal (i.e., elements from Group I of the PeriodicTable of the Elements), such as lithium, sodium, potassium, rubidium,cesium, and francium or may be a salt of calcium, silica or aluminum.The ionic compound may also be a nitrate, a fluoroborate, an ethanoate,a hexafluorophosphate or a halide. The ionic compound may have a meltingtemperature of less than or equal to four hundred degrees Celsius (400°C.) and, more particularly, between about twenty degrees Celsius (20°C.) and about three hundred degrees Celsius (300° C.). The cuttingelement 10 may be exposed to the ionic compound at a pressure of lessthan or equal to five kilobar (5 kbar) and, more particularly, betweenabout one-half of a kilobar (0.5 kbar) and about three kilobar (3 kbar).To remove the catalyst material 11 from the polycrystalline material 14,the ionic compound may be introduced to the polycrystalline material 14at a temperature of greater than or equal to a melting point of theionic compound. For example, the ionic compound may be heated to amolten state and the cutting element 10 may be immersed or dipped intothe molten ionic compound. The molten ionic compound may corrode,dissolve or otherwise remove the catalyst material 11 from a portion ofthe polycrystalline material 14 such that the interstices of the portionof the polycrystalline material 14 are substantially free of catalystmaterial 11.

In additional embodiments, the reactive material may include a leachingliquor that may dissolve the catalyst material 11 enabling removal ofthe catalyst material 11 from the cutting element 10. As used herein,the term “leaching liquor” means and includes liquid that may remove thecatalyst material 11 from the polycrystalline material 14 by, forexample, dissolving the catalyst material 11 or converting the catalystmaterial into a soluble salt. Suitable leaching liquors are known in theart and are described, by way of non-limiting example, in U.S. Pat. No.3,673,154 to Treyvillyan et al. (issued Jun. 27, 1972) and U.S. Pat. No.4,490,298 to Feld et al. (issued Dec. 25, 1984), the disclosure of eachof which is incorporated herein in its entirety by this reference. Forexample, the catalyst material 11 may be exposed to a leaching liquorformed by liquid phase oxidation of meta- or para-xylenes to isophthalicacid or terephthalic acid, with an oxidation catalyst (e.g., cobaltacetate) in the presence of an acetic acid solvent medium, which maydissolve the catalyst material 11 and form a phthalic acid. The phthalicacid, the acetic acid and water may be removed from the reaction mixtureand the resulting mixture may be treated with aqueous sodium carbonatesuch that a carbonate of the catalyst material 11 is formed. As anothernon-limiting example, the catalyst material 11 may be exposed to asolution of acetic acid and water and, thereafter, an oxalic acid oroxalic acid ester may be added to the solution to form an oxalate of thecatalyst material 11.

In further embodiments, the reactive material may be introduced to thepolycrystalline material 14 of the cutting element 10 in the form of aliquid fowling eutectic reaction. In some embodiments, a binary eutecticmay be formed by one or more rare earth elements, such as, germanium,yttrium, neodymium, cerium, and gadolinium. As a non-limiting example,the one or more elements may be liquefied by heating the one or moreelements to a temperature of greater than or equal to a melting pointthereof. For example, a germanium metal may be liquefied by heating to atemperature of about nine hundred thirty-eight degrees Celsius (938°C.). The liquefied element, such as liquid germanium, may be combinedwith about 15 wt % cobalt and cooled to a temperature of about sevenhundred thirty degrees Celsius (730° C.) to form a eutectic liquid,which remains a liquid as described in the phase diagram relationbetween cobalt and germanium. The phase diagram relation between cobaltand germanium is described in detail in, for example, K. Ishida and T.Nishizawa, Journal of Phase Equilibria, vol. 12, No. 1, pp. 77-83(1991), the entirety of which is incorporated herein by this reference.The cutting element 10 may be exposed to the eutectic liquid at apressure of less than or equal to about five kilobar (5 kbar) and, moreparticularly, between about one-half of a kilobar (0.5 kbar) and aboutthree kilobar (3 kbar). To remove the catalyst material 11 from thepolycrystalline material 14, the eutectic liquid may be introduced tothe polycrystalline material 14 at a temperature of greater than orequal to a melting point of an eutectic liquid phase. For example, afterforming the eutectic liquid, the cutting element 10 may be immersed ordipped into the eutectic liquid, which may be maintained in a moltenstate. The molten eutectic liquid may corrode, dissolve or otherwiseremove the catalyst material 11 from a portion of the polycrystallinematerial 14 such that the interstices of the portion of thepolycrystalline material 14 are substantially free of catalyst material11.

In yet further embodiments, the reactive material may be introduced tothe polycrystalline material 14 of the cutting element 10 in the form ofa chemical plasma. In some embodiments, the chemical plasma may includeone or more inert gases, such as, argon, nitrogen, helium, xenon,krypton and radon. In other embodiments, the chemical plasma may includean oxidizing agent, such as oxygen (O₂), ozone (O₃), fluorine (F₂),chlorine (Cl₂), peroxides, and the like. The chemical plasma may begenerated as known in the art in a conventional process of the typedescribed, by way of non-limiting example, in U.S. Pat. No. 4,494,620 toMatsuo et al. (issued Jan. 8, 1985), U.S. Pat. No. 4,361,472 to Morrison(issued Nov. 30, 1982), and H. Conrads and M. Schmidt, “PlasmaGeneration and Plasma Sources,” Plasma Sources Sci. Technol. 9:441-454(2000), the disclosure of each of which is incorporated herein in itsentirety by this reference. The cutting element 10 may be placed in achamber of a conventional plasma reactor and the chamber may be at leastpartially evacuated. One or more of the inert gases and the oxidizingagents may then be introduced into the plasma reactor and the chamber.The chemical plasma may be generated in a microwave electric field or ina high-frequency electric field under a reduced pressure. Thepolycrystalline material 14 may be used as a sputtering target and ionsin the chemical plasma may bombard the catalyst material 11 resulting inejection of the catalyst material 11 from the interstitial regions ofthe polycrystalline material 14. As a non-limiting example, an electricfield may be used to direct the ejected catalyst material 11 away fromthe cutting surface 18 of the polycrystalline material 14 and toward adummy plating material. By way of non-limiting example, the chemicalplasma may be contacted with the polycrystalline material 14 at atemperature of between about three hundred degrees Celsius (300° C.) andabout seven hundred fifty degrees Celsius (750° C.).

While the cutting element 10 may be exposed to the reactive material ata temperature of less than about four hundred degrees Celsius (400° C.)to prevent internal stress, the temperature of the reactive material maybe increased to less than or equal to about seven hundred fifty degreesCelsius (750° C.) to increase a rate of removal of the catalyst material11 from the polycrystalline material 14. The cutting elements 10, 10′formed according to embodiments of methods of the present disclosure mayprovide reduce the variation (i.e., the standard deviation) in depth ofremoval of the catalyst material 11 from the polycrystalline material 14of PDC cutting elements in comparison to the variation in the depth ofremoval of the catalyst material from PCD cutting elements usingconventional acid leaching process. For example, the standard deviationof the depth of removal of the catalyst material 11 throughout thepolycrystalline material 14 of PDC cutting elements (i.e., cuttingelement 10) may be reduced by between about 15% and about 20%. Inaddition, removal of the catalyst material 11 using the methods of thepresent disclosure may enable formation of the leached portion 28extending to a desired depth within the polycrystalline material 14without significant spikes or variations extending therepast. Formingthe cutting element 10 according to embodiments of the presentdisclosure enables removal of the catalyst material 11 from thepolycrystalline material 14 at reduced temperatures to prevent reversegraphitization of the polycrystalline material 14. Furthermore, formingthe cutting element 10 according to embodiments of the presentdisclosure substantially reduces or eliminates hazardous acid wastesthat are produced during conventional acid leaching processes.

FIG. 3A is an enlarged view illustrating how a microstructure of thepolycrystalline material 14 shown in FIGS. 2A and 2B may appear undermagnification. As shown in FIG. 3A, the polycrystalline material 14includes diamond crystals 30 that are bonded together by inter-granulardiamond-to-diamond bonds. The catalyst material 11 used to catalyze theformation of the inter-granular diamond-to-diamond bonds is disposed ininterstitial regions or spaces between the diamond crystals 30.

FIG. 3B is an enlarged view illustrating how a microstructure of thepolycrystalline material 14 shown in FIG. 2C may appear undermagnification. As shown in FIG. 3B, after removal of at least a portionof the catalyst material 11 using embodiments of the methods describedherein, cavities or voids 32 may be present in interstitial regions orspaces between the diamond crystals 30. The methods disclosed hereinenable removal of the catalyst material 11 from the polycrystallinematerial 14 at temperatures of less than or equal to seven hundred fiftydegrees Celsius (750° C.), which prevents internal stress within thecutting element (e.g., reverse graphitization) caused by increasedtemperatures.

FIG. 4 is a perspective view of an embodiment of an earth-boring rotarydrill bit 100 of the present disclosure that includes a plurality ofcutting elements 10 having a structure as shown in FIG. 2C, or otherpolycrystalline material structure having catalyst removed from one ormore portions thereof according to the disclosure. The earth-boringrotary drill bit 100 includes a bit body 102 that is secured to a shank104 having a threaded connection portion 106 (e.g., an AmericanPetroleum Institute (API) threaded connection portion) for attaching thedrill bit 100 to a drill string (not shown). In some embodiments, suchas that shown in FIG. 4, the bit body 102 may comprise a particle-matrixcomposite material, and may be secured to the metal shank 104 using anextension 108. In other embodiments, the bit body 102 may be secured tothe shank 104 using a metal blank embedded within the particle-matrixcomposite bit body 102, or the bit body 102 may be secured directly tothe shank 104.

The bit body 102 may include internal fluid passageways (not shown) thatextend between a face 103 of the bit body 102 and a longitudinal bore(not shown), which extends through the shank 104, the extension 108, andpartially through the bit body 102. Nozzle inserts 124 also may beprovided at the face 103 of the bit body 102 within the internal fluidpassageways. The bit body 102 may further include a plurality of blades116 that are separated by junk slots 118. In some embodiments, the bitbody 102 may include gage wear plugs 122 and wear knots 128. A pluralityof cutting elements 10′, as previously disclosed herein, may be mountedon the face 103 of the bit body 102 in cutting element pockets 112 thatare located along each of the blades 116. The cutting elements 10 arepositioned to cut a subterranean formation being drilled while the drillbit 100 is rotated under weight-on-bit (WOB) in a borehole aboutcenterline L₁₀₀.

Embodiments of cutting elements of the present disclosure also may beused as gauge trimmers, and may be used on other types of earth-boringtools. For example, embodiments of cutting elements of the presentdisclosure also may be used on cones of roller cone drill bits, onreamers, mills, bi-center bits, eccentric bits, coring bits, andso-called “hybrid bits” that include both fixed cutters and rollingcutters.

While the present disclosure has been described herein with respect tocertain embodiments, those of ordinary skill in the art will recognizeand appreciate that it is not so limited. Rather, many additions,deletions and modifications to the described embodiments may be madewithout departing from the scope of the disclosure as hereinafterclaimed, including legal equivalents. In addition, features from oneembodiment may be combined with features of another embodiment whilestill being encompassed within the scope of the disclosure ascontemplated by the inventors.

What is claimed is:
 1. A method of forming a polycrystalline compact foruse in an earth-boring tool, comprising: at least partially melting atleast one of a silicate glass, an alkali metal salt, and a rare earthelement to form a reactive material; introducing the reactive materialto a polycrystalline compact comprising a plurality of interstitialspaces between inter-bonded crystals of a polycrystalline materialthroughout which interstitial spaces a catalyst material is dispersed;and removing at least a portion of the catalyst material with thereactive material from at least a portion of the plurality ofinterstitial spaces.
 2. The method of claim 1, further comprising,before introducing the reactive material to the polycrystalline compact,forming a mask over at least a portion of at least one surface of thepolycrystalline compact, the mask comprising a material impervious tothe reactive material.
 3. The method of claim 1, wherein at leastpartially melting at least one of a silicate glass, an alkali metalsalt, and a rare earth element to form a reactive material comprises atleast partially melting at least one of a borosilicate glass, analuminosilicate glass, a phosphosilicate glass, and aborophosphosilicate glass to form the reactive material.
 4. The methodof claim 1, wherein at least partially melting at least one of asilicate glass, an alkali metal salt, and a rare earth element to form areactive material comprises heating the at least one of the silicateglass, the alkali metal salt, and the rare earth element to atemperature of greater than or equal to a melting point thereof.
 5. Themethod of claim 1, wherein at least partially melting at least one of asilicate glass, an alkali metal salt, and a rare earth element to form areactive material comprises at least partially melting an alkali saltcomprising at least one of lithium, sodium, potassium, rubidium, cesium,francium, calcium, silica, and aluminum to form the reactive material.6. The method of claim 1, wherein introducing the reactive material to apolycrystalline compact comprises introducing a reactive materialcomprising a molten lithium salt to the polycrystalline compactcomprising a plurality of interstitial spaces between inter-bondedcrystals of a polycrystalline material throughout which interstitialspaces, a catalyst material comprising cobalt is dispersed.
 7. Themethod of claim 1, wherein introducing the reactive material to apolycrystalline compact comprises introducing a molten silicate glass tothe polycrystalline compact comprising a plurality of interstitialspaces between inter-bonded crystals of a polycrystalline materialthroughout which interstitial spaces, a catalyst material comprisingcobalt is dispersed.
 8. The method of claim 7, wherein introducing amolten silicate glass to the polycrystalline compact comprising aplurality of interstitial spaces between inter-bonded crystals of apolycrystalline material throughout which interstitial spaces, acatalyst material comprising cobalt is dispersed comprises introducingthe molten silicate glass to the polycrystalline compact at atemperature of less than about 1000° C.
 9. The method of claim 1,wherein introducing the reactive material to a polycrystalline compactcomprising a plurality of interstitial spaces between inter-bondedcrystals of a polycrystalline material throughout which interstitialspaces, a catalyst material is dispersed comprises introducing thealkali metal salt to a polycrystalline compact comprising a catalystmaterial at a temperature of less than or equal to 400° C.
 10. A methodof forming a polycrystalline compact for use in an earth-boring tool,comprising: at least partially melting a rare earth element to form areactive material; and introducing the reactive material to apolycrystalline compact comprising a catalyst material disposed ininterstitial spaces between inter-bonded crystals of a polycrystallinematerial to remove at least a portion of the catalyst material, whereinat least partially melting a rare earth element to form a reactivematerial comprises at least partially melting a plurality of rare earthelements to form a binary eutectic liquid.
 11. The method of claim 10,wherein at least partially melting a plurality of rare earth elements toform a binary eutectic liquid comprises at least partially melting theplurality of rare earth elements to form at least one of acobalt-germanium eutectic, cobalt-neodymium eutectic, cobalt-yttriumeutectic, cobalt-cerium eutectic, and cobalt-gadolinium eutectic.
 12. Amethod of forming a polycrystalline compact cutting element for anearth-boring tool, comprising: forming a cutting element comprising apolycrystalline material and a catalyst material disposed ininterstitial spaces between inter-bonded crystals of the polycrystallinematerial; and removing at least a portion of the catalyst material fromthe interstitial spaces by exposing at least a portion of thepolycrystalline material to a chemical plasma comprising an inert gas oran oxidizing agent, wherein removing at least a portion of the catalystmaterial from the interstitial spaces by exposing at least a portion ofthe polycrystalline material to a chemical plasma comprises introducingat least one surface of the polycrystalline material to a chemicalplasma comprising at least one of argon, nitrogen, helium, xenon,krypton, and radon.
 13. The method of claim 12, wherein introducing atleast one surface of the polycrystalline material to a chemical plasmacomprising at least one of argon, nitrogen, helium, xenon, krypton, andradon comprises introducing at least one surface of the polycrystallinematerial to the chemical plasma at a temperature of between about 300°C. and about 750° C.
 14. A method of forming a polycrystalline compactcutting element for an earth-boring tool, comprising: forming a cuttingelement comprising a polycrystalline material and a catalyst materialdisposed in interstitial spaces between inter-bonded crystals of thepolycrystalline material; and removing at least a portion of thecatalyst material from the interstitial spaces by exposing at least aportion of the polycrystalline material to a chemical plasma comprisingan inert gas or an oxidizing agent, wherein removing at least a portionof the catalyst material from the interstitial spaces by exposing atleast a portion of the polycrystalline material to a chemical plasmacomprises introducing at least one surface of the polycrystallinematerial to a chemical plasma comprising at least one of oxygen, ozone,fluorine, chlorine, and a peroxide.